1. Field of the Invention
In internal combustion engines, reservoir injection systems (common rail systems) are increasingly used today; they make it possible to adjust the injection pressure independently of rpm and load. In common rail systems, the pressure generation and the injection event are decoupled from one another both chronologically and in terms of location. The injection pressure is generated by a separate high-pressure pump. This pump need not necessarily be driven synchronously with the injections. The pressure can be adjusted independently of the engine rpm and the injection quantity. In common rail systems, instead of pressure-controlled injection valves, electrically actuated injectors are used, with which the triggering instant and duration of triggering, the injection onset, and the injection quantity can be determined. In this type of injection system, there is great freedom with regard to the design of multiple injections or subdivided injections.
2. Prior Art
Fuel injectors for reservoir injection systems are as a rule triggered via solenoid valves or piezoelectric actuators. By means of the solenoid valves or piezoelectric actuators, a pressure relief of a control chamber is effected. To that end, the control chamber has a relief conduit, in which as a rule there is an outlet throttle. Filling the control chamber for actuating the injection valve member is as a rule done via an inlet from valve associated with the control chamber, or the piezoelectric actuator associated with it, a valve closing member is actuated, which closes the outflow conduit. Upon actuation of the solenoid valve or piezoelectric actuator, the valve closing member, which may for example be a ball body or a cone, uncovers the outflow conduit, so that a control volume is capable of flowing out of the control chamber. As a result, the pressure in the control chamber drops, and an injection valve member, as a rule embodied as a needle, acted upon by the control chamber moves vertically upward. As a result of the upward motion of the injection valve member, injection openings on the end of the fuel injector toward the combustion chamber are uncovered, so that fuel can be injected into the combustion chamber of an internal combustion engine.
The fuel injectors known from the prior art, which are actuatable via solenoid valves or piezoelectric actuators, as a rule include an injector body, which is constructed in pressureproof and pressuretight fashion. The solenoid valve or piezoelectric actuator is received outside this injector body. As a result, the pressure level in the control chamber is lowered via the opening of the outflow conduit. On this principle, an actuation of the needle-like injection valve member is effected indirectly. A hydraulic booster device is as a rule associated with the piezoelectric actuator that is located outside the valve body, so that the stroke travel of the piezoelectric actuator can be lengthened, since the piezoelectric crystals, in stacked form, when supplied with current have only a slight change in length. If conversely the fuel injector is actuated via a solenoid valve, then it is necessary that its remnant air gap and armature stroke travel be adjusted exactly, in order to trigger the valve closing member, which closes the outflow conduit of the control chamber, suitably precisely, particularly in the high rpm range of an internal combustion engine.
Because of the trigger devices, that is, a solenoid valve or piezoelectric actuator, that are located outside the injector body, the fuel injectors known from the prior art are relatively tall and accordingly require greater installation space in the region of the cylinder head of an engine. The trend in modem engines, however, is to increasingly less available installation space in the region of the cylinder head. This is associated with the fact that internal combustion engines with high specific power per liter of displacement require more-complicated cooling of the cylinder head region. This is done as a rule through conduits that penetrate the cylinder head of the engine and that both for thermal reasons and for reasons of thermal conductivity have a certain course. As a result, the installation space required for installing fuel injectors is reduced, and there is accordingly a need for developing other solutions to the problem.